1. Field of the Invention
The present invention relates to a steering system for a small-sized vehicle such as a saddle type three-wheel vehicle or four-wheel vehicle used for farming, an ATV (All Terrain Vehicle) for sportive traveling off-road, a golf cart, and other suitable vehicles. More specifically, the present invention relates to a steering system having a power steering apparatus.
2. Description of the Related Art
Generally, a small-sized vehicle used for traveling off road has the following structure. Front and rear wheels, each having a balloon tire with low pressure and wide diameter, are disposed at the front and rear of a vehicle body frame, and an engine unit is mounted between the front and rear wheels. Furthermore, a steering shaft is arranged between the left and right front wheels, and a wheel-type steering handle or a bar-type steering handle is attached to the upper end of the steering shaft. Such a small-sized vehicle can travel off road at will by turning the steering handle from side to side.
In recent years, some users have demanded further improvements in operability when maneuvering the small-sized vehicle to reduce a load on operating the steering handle.
Accordingly, a power steering apparatus that is connected to the steering shaft has been suggested to provide an assisting steering force by this power steering apparatus.
Where the above-described power steering system is provided, a structure is adopted in which an input shaft (which is an input unit of a direct steering force by an operator) of a reduction gear of the power steering apparatus is coupled to a lower end of the steering shaft, and an output shaft of the reduction gear (which is an output unit of the resultant force of the direct steering force and the assisting steering force) is coupled to a tie rod via a link mechanism. In such a structure, the steering shaft and the input shaft of the above-described reduction gear must be coaxially arranged with high accuracy so as to facilitate turning of the steering shaft. On the other hand, a vehicle body frame on which the above-described steering shaft and reduction gear are mounted is generally manufactured by bending and forming steel pipes into desired shapes and joining them by welding or the like, such that the dimensional accuracy thereof is not very high. Therefore, it is difficult to coaxially arrange the above-described steering shaft and reduction gear with high accuracy.